The goal of this project is to determine whether artificial menstrual cycles in ovariectomized monkeys could support implantation and pregnancy after transfer of cryopreserved, in vitro fertilization-produced embryos. Spayed, rhesus monkeys first received a 3 cm estradiol (E) implant (day 0). On days 9-13, increasing doses of E were injected to simulate the estradiol surge. To mimic P levels during the luteal phase, a 3 cm progesterone (P) implant was placed sc on day 14 followed by a second P implant on day 17; one P implant was removed on day 24, and the second on day 28 with induction of menses within 2 days. A second artificial cycle was administered, with embryo transfers performed on day 17. Embryo donors received either urinary or recombinant human follicle stimulating hormone q human luteinizing hormone to stimulate the growth of multiple follicles, followed by urinary or recombinant human chorionic gonadotropin (hCG) to induce ovulatory maturation. Mature oocytes were harvested 27 h post-hCG, and inseminated in vitro. Resultant embryos were cryopreserved, then thawed prior to transfer at the 2- to 4-cell stage (2-3 embryos/recipient). In Phase 1 of this study, 4 recipients underwent sequential oviductal followed by transcervical embryo transfer. Biochemical pregnancy, associated with increases in circulating bioactive macaque CG for up to 36 days of gestation, was noted in 1/4 recipients after oviductal and 1/4 after transcervical transfer of embryos derived from urinary gonadotropin treatment. Following 11 oviductal transfers (n=5-6 recipients) of embryos derived from recombinant human gonadotropin stimulation in Phase 2, one singleton pregnancy resulted in delivery of a normal stillborn female on day 132 of gestation. In Phase 3, oviductal transfer of recombinant human gonadotropin-derived embryos to 4 recipients yielded one singleton pregnancy that is currently ongoing. Thus, implantation and pregnancy can occur when IVF-produced, cryopreserved embryos are transferred during artificial menstrual cycles in spayed rhesus monkeys. Current efforts are aimed at improving implantation efficiency through further optimization of this animal model.